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Molecular and Cellular Biology, October 2005, p. 9103-9114, Vol. 25, No. 20
0270-7306/05/$08.00+0 doi:10.1128/MCB.25.20.9103-9114.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
and
Katherine L. Friedman*
Vanderbilt University, Department of Biological Sciences, VU Station B, Box 351634, Nashville, Tennessee 37235
Received 12 January 2005/ Returned for modification 7 March 2005/ Accepted 21 July 2005
Telomerase is a reverse transcriptase that maintains chromosome integrity through synthesis of repetitive telomeric sequences on the ends of eukaryotic chromosomes. In the yeast Saccharomyces cerevisiae, telomere length homeostasis is achieved through negative regulation of telomerase access to the chromosome terminus by telomere-bound Rap1 protein and its binding partners, Rif1p and Rif2p, and positive regulation by factors such as Ku70/80, Tel1p, and Cdc13p. Here we report the identification of mutations within an N-terminal region (region I) of the yeast telomerase catalytic subunit (Est2p) that cause telomere lengthening without altering measurable catalytic properties of the enzyme in vitro. These telomerase mutations affect telomere length through a Ku-independent mechanism and do not alter chromosome end structure. While Tel1p is required for expression of the telomere-lengthening phenotype, Rif1p and Rif2p are not, suggesting that telomere overextension is independent of Rap1p. Taken together, these data suggest that specific amino acids within region I of the catalytic subunit of yeast telomerase play a previously unanticipated role in the response to Tel1p regulation at the telomere.
Supplemental material for this article may be found at http://mcb.asm.org/.
Present address: Emory University, Yerkes National Primate Research Center, 954 Gatewood Road NE, Atlanta, GA 30322.
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